2001; Wawrzyniak et al. 2008). The chlorosome antennae In contrast to the antenna apparatus of all ON-01910 other photosynthetic organisms, the heterogeneous chlorosome antennae of green photosynthetic bacteria contain rod-shaped

oligomers of BChl-c/d/e molecules that self aggregate without assistance of a protein. Their structural functional features have been the inspiration for self-assembled artificial antennae (Ganapathy et al. 2009b; Oostergetel et al. 2010; Balaban et al. 2005). The π–π interactions of overlapping macrocycles from the adjacent BChls give rise to ring-current shifts; an effect in BIIB057 purchase which the electronic ring current of the macrocycles induces

a local magnetic field that affects the NMR chemical shifts of the adjacent BChl in the structure with molecular overlap. The magnitudes of the ring-current shifts together with long-range 1H-13C correlations provide constraints for the packing mode of the BChls in the macrostructures (van Rossum et al. 2002). In conjunction with distance constraints from diffraction techniques and computational modeling, this provided a method to solve a template for the chlorosome self-assembled structure in detail. By constructing a triple mutant, the Anacetrapib heterogeneous BChl-c pigment composition of chlorosomes of the green sulfur bacteria Chlorobaculum tepidum was simplified to nearly homogeneous BChl d. Computational integration of solid-state NMR and cryo-electron microscopy revealed a BI 10773 mw syn-anti stacking mode and led to a structural model of BChls self-assembled into coaxial cylinders to form tubular-shaped elements. (Ganapathy et al. 2009a). The macrostructures are stabilized by C=O∙∙H–O∙∙Mg interactions between the 31 hydroxy group, the 13 carbonyl and the central magnesium, and by π–π interactions between

the tetrapyrrole macrocycles (Fig. 3). Since low-lying CT states are an intrinsic property of higher aggregates of chlorophyll molecules and are likely to mix significantly with the exciton states, the polarizability effects in chlorosome aggregates are strongly enhanced compared to BChl-c monomers. The structural framework can accommodate chemical heterogeneity in the side chains for adaptive optimization of the light-harvesting functionality by optical tuning and broadening. In addition, the BChls form sheets that allow for strong exciton overlap in two dimensions, enabling triplet exciton formation for photo protection. Fig.